This invention relates to continuous production of vinegar resulting from the microbiological conversion of ethanol into acetic acid.
The method currently used consists of fermentation in immersed culture, with strong aeration by air. Ethanol, of microbiological or chemical origin, is converted by acetic fermentation in the presence of microorganisms of the Acetobacter type, according to the reaction: EQU C.sub.2 H.sub.5 OH+O.sub.2 .fwdarw.CH.sub.3 COOH+H.sub.2 O
into vinegars of wine, alcohol, cider, malt, milk, etc . . . .
Around 1950, HROMATKA found that during the preparation of vinegar in immersed culture, the consumption of oxygen was able to reach 7.75 liters per dry-weight gram of bacteria per hour. According to U.S. Pat. No. 2,707,683, the addition of oxygen necessary for bacteria is performed by insufflation of air during fermentation.
In general, acetic fermentation is performed primarily semi-continuously and sometimes continuously.
The use of oxygen enriched air has been described in French Pat. No. 2,331,616.
Industrially, in the present state of the art, only fermentation where desired metabolite is known as primary, can be performed continuously. This process exhibits the advantage of a gain in productivity due particularly to the absence of time losses at filling, bleeding, cleaning of fermenting rooms and phases of latency and exponential multiplication of the microrganisms, In the case of production of acetic acid, the productivity reached is on the order of 1.4 g/l.hr.
However, this process is limited by an insufficient aeration resulting from a lack of oxygen available in the dissolved state of the reactor, and by the inhibition of the growth of the microorganisms due to the substrate, with an alcohol base from 30 g/l, and by the acetic acid produced inhibiting product of the growth at least partially, regardless of its concentration, and totally beyond 80 g/l.
Moreover, the techniques of batch production of acetic acid have productivities depending on the processes, equal to 1 to 1.5 g/l.h for immersed cultures, and 0.25 g/l.h for the cultures with trickling over chips.
Oxygen enrichment of these two main processes at best makes it possible only to double the respective productivities. The arguments of the performances are reflected by a shortening of the time of the cycles.
Additionally, the standard techniques for continuous production of vinegar with oxygen enrichment make it possible to obtain 2 g of acid per liter per hour.
Further, only a rise in the partial pressure of oxygen in the aeration gas could lift the limitation due to oxygen, because a rise in the gas flow would bring out an evaporation of substrate and product produced. A packing that fills the reactor cannot be considered because it would oppose the transfer of oxygen. In addition, the use of naturally flocculant strains does not add any stability during the hydrodynamic flowing.